全文获取类型
收费全文 | 1331079篇 |
免费 | 29557篇 |
国内免费 | 7720篇 |
专业分类
化学 | 665479篇 |
晶体学 | 20199篇 |
力学 | 74386篇 |
综合类 | 101篇 |
数学 | 240919篇 |
物理学 | 367272篇 |
出版年
2021年 | 13494篇 |
2020年 | 15924篇 |
2019年 | 16064篇 |
2016年 | 27571篇 |
2015年 | 20671篇 |
2014年 | 30393篇 |
2013年 | 74332篇 |
2012年 | 37626篇 |
2011年 | 33969篇 |
2010年 | 36498篇 |
2009年 | 38894篇 |
2008年 | 33498篇 |
2007年 | 28927篇 |
2006年 | 36013篇 |
2005年 | 27698篇 |
2004年 | 29344篇 |
2003年 | 27954篇 |
2002年 | 29137篇 |
2001年 | 28070篇 |
2000年 | 24556篇 |
1999年 | 22439篇 |
1998年 | 20951篇 |
1997年 | 21019篇 |
1996年 | 21103篇 |
1995年 | 19189篇 |
1994年 | 18628篇 |
1993年 | 18178篇 |
1992年 | 18087篇 |
1991年 | 18390篇 |
1990年 | 17609篇 |
1989年 | 17692篇 |
1988年 | 17217篇 |
1987年 | 17183篇 |
1986年 | 16134篇 |
1985年 | 22534篇 |
1984年 | 23794篇 |
1983年 | 19982篇 |
1982年 | 21684篇 |
1981年 | 20905篇 |
1980年 | 20260篇 |
1979年 | 20431篇 |
1978年 | 21730篇 |
1977年 | 21329篇 |
1976年 | 21109篇 |
1975年 | 19756篇 |
1974年 | 19489篇 |
1973年 | 19962篇 |
1972年 | 14406篇 |
1968年 | 12245篇 |
1967年 | 12584篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Clifford S. Queen 《Journal of Number Theory》2002,92(1):164-173
In this paper we develop a theory of unique factorization for subgroups of the positive rationals. We show that this theory is strong enough to include arithmetic progressions and the theory of genera in algebraic number fields. We establish generalizations of both Dirichlet's theorem on primes in arithmetic progressions and the theory of genera for Abelian extensions of the rationals. 相似文献
982.
X. Dong 《Discrete and Computational Geometry》2002,27(1):85-97
We prove that the homotopy types of two naturally defined simplicial complexes are related in the following way: one is homotopy
equivalent to a multiple suspension of the canonical Alexander dual of the other. These simplicial complexes arise in free
resolutions of semigroup rings and modules. The relation between their homotopy types was conjectured by Reiner, and was suggested
by a homological consequence of a result due independently to Danilov and Stanley on canonical modules of normal semigroup
rings. Our proof is purely topological, and gives an alternative proof of their result. We also prove a generalization of
a result of Hochster saying that these rings are Cohen—Macaulay, and indicate a new proof of Ehrhart's reciprocity law for
rational polytopes.
Received October 3, 2000, and in revised form April 2, 2001, and May 10, 2001. Online publication November 7, 2001. 相似文献
983.
We call a one-way infinite word w over a finite alphabet (ρ,l)-repetitive if all long enough prefixes of w contain as a suffix a ρth power (or more generally a repetition of order ρ) of a word of length at most l. We show that each (2,4)-repetitive word is ultimately periodic, as well as that there exist continuum many, and hence also nonultimately periodic, (2,5)-repetitive words. Further, we characterize nonultimately periodic (2,5)-repetitive words both structurally and algebraically. 相似文献
984.
Y.Y. Lee 《Applied Acoustics》2002,63(11):1157-1175
The nonlinear natural frequency of a rectangular box, which consists of one flexible plate and five rigid plates, is studied in this paper. The flexible plate is assumed to vibrate like a simple piston. The behavior of the structural-acoustic coupling between the flexible plate and the air cavity is analyzed by using the proposed finite element modal method. The system finite element equation is reduced and expressed in terms of the modal coordinates with small degrees of freedom by using the proposed reduction method. The system nonlinear stiffness matrix representing the large amplitude vibration can be transformed to be a constant modal matrix. The natural frequencies are determined by using the harmonic balance method to solve the eigenvalue equations of the structural-acoustic system. The effect of the cavity depth on the natural frequencies and convergence studies are discussed in detail. 相似文献
985.
Possible Loss and Recovery of Gibbsianness¶During the Stochastic Evolution of Gibbs Measures 总被引:1,自引:1,他引:0
A.C.D. van Enter R. Fernández F. den Hollander F. Redig 《Communications in Mathematical Physics》2002,226(1):101-130
We consider Ising-spin systems starting from an initial Gibbs measure ν and evolving under a spin-flip dynamics towards a
reversible Gibbs measure μ≠ν. Both ν and μ are assumed to have a translation-invariant finite-range interaction. We study
the Gibbsian character of the measure νS(t) at time t and show the following:
(1) For all ν and μ, νS(t) is Gibbs for small t.
(2) If both ν and μ have a high or infinite temperature, then νS(t) is Gibbs for all t > 0.
(3) If ν has a low non-zero temperature and a zero magnetic field and μ has a high or infinite temperature, then νS(t) is Gibbs for small t and non-Gibbs for large t.
(4) If ν has a low non-zero temperature and a non-zero magnetic field and μ has a high or infinite temperature, then νS(t) is Gibbs for small t, non-Gibbs for intermediate t, and Gibbs for large t.
The regime where μ has a low or zero temperature and t is not small remains open. This regime presumably allows for many different scenarios.
Received: 26 April 2001 / Accepted: 10 October 2001 相似文献
986.
In this paper we introduce a generalization of stable sets: stable multi-sets. A stable multi-set is an assignment of integers
to the vertices of a graph, such that specified bounds on vertices and edges are not exceeded. In case all vertex and edge
bounds equal one, stable multi-sets are equivalent to stable sets.
For the stable multi-set problem, we derive reduction rules and study the associated polytope. We state necessary and sufficient
conditions for the extreme points of the linear relaxation to be integer. These conditions generalize the conditions for the
stable set polytope. Moreover, the classes of odd cycle and clique inequalities for stable sets are generalized to stable
multi-sets and conditions for them to be facet defining are determined.
The study of stable multi-sets is initiated by optimization problems in the field of telecommunication networks. Stable multi-sets
emerge as an important substructure in the design of optical networks.
Received: February 14, 2001/Revised version: September 7, 2001 相似文献
987.
Michael K. Kinyon Kenneth Kunen J. D. Phillips 《Proceedings of the American Mathematical Society》2002,130(3):619-624
An A-loop is a loop in which every inner mapping is an automorphism. A problem which had been open since 1956 is settled by showing that every diassociative A-loop is Moufang.
988.
989.
C.-C. WANGZ. YE 《Journal of sound and vibration》2002,250(4):723-744
The oscillation of a bubble has many vibrational modes, contributing to different portions in acoustic scattering. Without approximations a priori, an hydrodynamic approach is applied to investigate acoustic scattering by a bubble in water, taking into account the heat exchange and viscosity. The scattering function is derived for a wide range of frequencies. Examples are shown to illustrate the thermal and viscous effects on sound scattering. Comparison is made with three existing models. While these models are known not to be applicable for high frequencies, it is shown here that even in the low-frequency region, there are also noticeable discrepancies between the exact solution and the three existing models with regard to the scattering properties such as the scattering cross-section, and the quality factor of resonant peaks. By numerical simulation, we claim that the discrepancies may be due to the incomplete consideration of the thermal exchange process in the previous models. The approach presented here is valid for any other fluid enclosure in liquids. 相似文献
990.
P. Adamson 《Optics & Laser Technology》2002,34(7):561-568
The differential reflection characteristics for ultrathin inhomogeneous dielectric film on absorbing substrate are investigated in the long-wavelength approximation. The obtained first-order expressions for differential reflectivity and changes in the ellipsometric angles caused by ultrathin layer are of immediate interest to the solution of the inverse problem. The method to determine the averaged values (not the realistic profile) of refractive index for inhomogeneous nanometric films are shown. The novel possibilities for determining the dielectric constant and thickness of nanoscale homogeneous films by the differential ellipsometric and reflectivity measurements are developed, and a simple method to estimate whether the nanometric film is homogeneous or not is also discussed. 相似文献